<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
<script>
let num = +prompt('请您输入您的成绩')
if(num >90){
    alert('优秀')
}
else if(num>=70 ){
    alert('良好')
}
else if(num>=60 ){
    alert('及格') 
}
else{
    alert('不及格')
}
</script>
</html>